Nanami Kanroji is a secondary character in School Days. She is a student in class 1-3 of Sakakino High and is part of Sekai Saionji's circle of friends. She was admitted to the school on a scholarship due to her athletic talent and is a member of the school's basketball team, where she is considered popular and the center of her friend group. Nanami previously attended the same middle school as Kotonoha Katsura. She has a younger sister named Yae. Her boyfriend is a senior in the basketball club and is described as a hardcore otaku, a detail that leads others to question her taste in partners.

Nanami possesses an intense, love-or-hate personality. She is fiercely loyal and caring toward those she likes, but treats those she dislikes with complete coldness and barely restrains her emotions. Her candid, unfiltered attitude wins admiration from some while deeply alienating others. Despite a surface-level maturity, she can be biased, presumptuous, and petty—traits that emerge notably in her treatment of Kotonoha. As a scholarship athlete, Nanami wields significant influence over sports clubs at the school. In several story routes of the visual novel, she uses this power to orchestrate bullying against Kotonoha, though the anime adaptation limits this to minor verbal antagonism. She becomes extremely upset when a sex tape featuring her and her boyfriend is shown to many classmates as a cruel joke after the school festival.

Nanami's role in the story is primarily as a friend and ally of Sekai, and she often behaves coldly toward Makoto Itou, believing him to be dating her friend. Her relationships are defined by her strong loyalty to Sekai and her antagonism toward Kotonoha. She does not undergo significant personal development over the course of the narrative. Her notable abilities are limited to her athletic prowess, particularly in basketball, and her social influence within the school's sports clubs.